1. Field of the Invention
The present invention relates to a liquid leakage detector for detecting leakage of a liquid, such as contaminated liquids, a liquid transport apparatus which incorporates the liquid leakage detector, and a method of detecting liquid leakage.
2. Description of the Related Art
From the viewpoint of safety or environmental conservation, there is an increasing demand for techniques to detect leakage of liquids, such as organic solvents and contaminated liquids of chemicals. A configuration using plastic clad fiber (PCF) has been proposed as one of the leakage detection techniques. The PCF-based technique employs an optical fiber constituted by a core and a cladding which wraps the core. The cladding is made of a light absorbing material. Leakage is detected based on an increase in light propagation loss in the optical fiber due to a change in the refractive index of the cladding to which the liquid adheres or through which the liquid permeates. In addition to the detection of liquid leakage, a site of leakage is detected in this technique by determining a distribution of propagation loss in the direction of a light beam path in the using, for example, an optical time-domain reflectmeter (OTDR) device.
Japanese Patent Laid-Open No. 63-266340 proposes a technique of detecting liquid leakage based on an increase in propagation loss when an optical fiber is bent using a material which swells when a liquid permeates the same.
Recently, inkjet printers, which were typically intended for home use, have been applied to a wide variety of fields; in the business field, inkjet printers are used in offices or for retail photographing and, in the industrial field, inkjet printers are used for drawing electronic circuits and manufacturing flat panel displays. Inkjet printers for business use should have high speed printing performance. In such high speed printing, however, in the event that ink leakage occurs in an ink supply unit, the leakage should be detected promptly and the recording operation should be stopped immediately; otherwise, defective printed matters will increase in number in a short time and, as a result, users will suffer serious loss in their commercial products.
Since printers for business use should be equipped with a large-sized ink tank for mass printing, an “off-carriage” system is often employed in which recording heads are separated from the ink tank and ink is supplied through an ink tube. In some printers employing this system, the recording heads are connected to the ink tank via the ink tube and the ink tank is pressurized to supply the ink to the recording heads. In such printers, even a very small amount of ink leakage may easily scatter inside the printer, which leads to a possibility of contamination inside the printer and an increased range of corrosion damage of the printer. For this reason, it is required to detect ink leakage promptly and correctly. In the printers for business use, unlike printers for consumer use, there is a demand for shorter standby time and longer print operation time in order for improved equipment operation efficiency. For this reason, a technique of constant detection of ink leakage without any interruption of ink supply is required in the printers for business use.
The following methods, for example, have been proposed for constant detection of ink leakage during the supply of ink:    1. detecting leakage of ink at an electrode for leakage detection using electrical conductivity of ink (U.S. Pat. No. 6,402,277 and Japanese Patent No. 3162547);    2. detecting leakage of ink by detecting changes in reflectivity or an amount of transmitted light in an ink detection unit (Japanese Patent No. 3288921); and    3. detecting leakage of ink using an ink detection member which changes in shape when brought into contact with ink (Japanese Patent Laid-Open No. 06-340089 and Japanese Patent Laid-Open No. 2006-231803).
In the configuration of the PCF-based liquid leakage detector and the configuration proposed in Japanese Patent Laid-Open No. 63-266340 described above, however, have a deficiency that false detection of leakage will be made when the configuration is applied to monitoring leakage in the pipe of liquids, such as contaminated waste water. That is, these configurations may detect adhesion of liquid droplets to the PCF or a swelling material caused by high humidity or dew condensation in a surrounding environment of the pipe for the liquid as liquid leakage when no leakage occurs actually.
In inkjet printers, ink droplets are normally floating as fine mist which adheres to and deposit on surfaces of various members constituting the printers. For this reason, there is a possibility that the configurations proposed in the Patent Documents mentioned above make false detection of ink leakage when the ink mist adheres to and deposit on the liquid detection unit.